The present invention relates to a planar light-emitting display panel device or, more particularly, to a planar light-emitting framed display panel device belonging to the so-called edge-lighting system in which an image borne on a transparency such as landscapes, portraits, commercial goods and the like is illuminated from behind on a planar light-emitting board so that the image is imparted with clear conspicuousness with ready replaceability of the image-bearing transparency enabling exhibition of a variety of images to meet the requirements of the occasions and places.
It is very conventional from old that panels of paintings or photographs either unframed or framed are used for the purpose of room decoration and commercial advertisement. The most traditional way to make the images of paintings or photographs conspicuous to the viewers is limited to illumination of the painting or photograph by projecting light to the surface of the painting or photograph to increase the luminosity of the surface despite the limited effectiveness of the method.
Alternatively, backlight-illuminated display panels are also known mainly for the purpose of commercial advertisement in which an image-bearing transparency is illuminated by light from behind so that the image borne on the transparency is made conspicuous. Since the light source used in the display panels of this type is limited to an assembly of a plurality of linear light sources such as fluorescent lamps, however, the surface luminosity of the display panel cannot be very uniform over the whole surface, display panels of this type are not always quite satisfactory when a high aesthetic effect is desired as in the appreciation of fine art masterpieces of landscapes, portraits and the like.
On the other hand, a planar light-emitting display system to serve as a backlight for liquid crystal panels by the so-called edge-lighting system, which ensures uniformity of luminosity over the whole surface, has made its debut as a result of recent development works. An attempt is also made for the utilization of the same as a planar light source for illumination of an image-bearing transparency from behind.
The above mentioned planar light-emitting system of the edge-lighting type is disclosed in Japanese Patent Kokai 3-118594 and U.S. Pat. No. 5,283,673, according to which a light-conductive board made from a transparent material is illuminated at one or opposite two of the edge surfaces each by projecting light from a linear light source such as an elongated fluorescent lamp to make planar light emission by means of the light transmitting the light-conductive board from one of the flat surfaces. The luminosity of the surface naturally decreases from the surface of the light incidence to the position remote therefrom so that the luminosity of the surface cannot be uniform enough. This problem of non-uniformity of the surface luminosity is compensated for by providing an irregular-reflection or light-scattering layer having a gradation on one of the surfaces of the light-conductive board by the method of special printing or embossing.
In the prior art backlight illumination unit of images utilizing the planar light-emitting system of the edge-lighting type, however, a specific image and a light-emitter are in a fixedly conjoined structure so that a picture scene of the image can be changed to a different one only by replacing the unit as a whole with a great inconvenience.
The present invention has an object, in view of the above described disadvantages and inconveniences in the prior art, to provide a planar light-emitting display panel device of the edge-lighting type in which a transparency bearing an image of landscape, portrait and the like is uniformly illuminated from behind so as to clearly make the image conspicuous without decreasing the aesthetic value of the image along with ready replaceability of the image-bearing transparency at any time as desired.
Thus, the present invention provides a planar light-emitting display panel device of the edge-lighting type which comprises, as an assembly:
a planar light emitter (6) comprising a light-conductive board (1);
at least one elongated light source (7) which is in contact with or in the vicinity of one of the edge surfaces of the light-conductive board (1);
a transparency sheet (15) bearing an image as mounted on the planar light emitter; and
a rectangular frame (11) consisting of four frame branches having an inversely L-shaped cross section fixedly holding the planar light emitter (6) and the image-bearing transparency sheet (15) at three frame branches (8, 9, 10), the rest of the frame branches (11) being openable and closable, in which engagement grooves (12, 13, 14) are defined by the lower surface of the top flat of each of the three frame branches (8, 9, 10) and the upper surface of the planar light emitter (6), the elongated light source (7) is located in the space between one of the frame branches and the edge surface of the light-conductive board (1) and the image-bearing transparency sheet (15) is, either as such or as being held by a folder made of a transparent plastic sheet (16), inserted into the engagement grooves (12, 13, 14) in a freely withdrawable fashion.